1. Field of the Invention
The present invention relates to an optical image measurement device and an optical image measurement method for forming an image of an eye by projecting a light beam to the eye and using a reflected light therefrom.
2. Description of the Related Art
In recent years, attention has been focused on an optical image measurement technique of forming an image showing the surface morphology or internal morphology of a measurement object by using a light beam from a laser light source or the like. Because this optical image measurement technique does not have invasiveness to human bodies unlike an X-ray CT device, it is expected to employ this technique particularly in the medical field.
Japanese Unexamined Patent Application Publication JP-A 11-325849 discloses an optical image measurement device configured in a manner that: a measuring arm scans an object by using a rotary deflection mirror (Galvano mirror); a reference mirror is disposed to a reference arm; at the outlet thereof, such an interferometer is used that the intensity of a light caused by interference of light fluxes from the measuring arm and the reference arm is analyzed by a spectrometer; and the reference arm is provided with a device gradually changing the light flux phase of the reference light in non-continuous values.
The optical image measurement device disclosed in JP-A 11-325849 uses a method of so-called “Fourier Domain OCT (Optical Coherence Tomography).” That is to say, the morphology of the measurement object in the depth direction (z-direction) is imaged by applying a beam of a low-coherence light to a measurement object, obtaining the spectrum intensity distribution of the reflected light, and subjecting the obtained distribution to Fourier transform.
Furthermore, the optical image measurement device described in JP-A 11-325849 is provided with a Galvano mirror scanning with a light beam (a signal light), thereby being capable of forming an image of a desired measurement region of a measurement object. Because this optical image measurement device scans with the light beam only in one direction (x-direction) orthogonal to the z-direction, a formed image is a 2-dimensional tomographic image in the depth direction (z-direction) along the scanning direction of the light beam (the x-direction).
Further, Japanese Unexamined Patent Application Publication JP-A 2002-139421 discloses a technique of scanning with a signal light in both the horizontal and vertical directions to thereby form a plurality of 2-dimensional tomographic images in the horizontal direction and, based on these plurality of tomographic images, acquiring and imaging 3-dimensional tomographic information of a measurement range. A method for 3-dimensional imaging is, for example, a method of arranging and displaying a plurality of tomographic images in the vertical direction (referred to as stack data or the like), and a method of forming a 3-dimensional image by subjecting a plurality of tomographic images to a rendering process.
Further, Japanese Unexamined Patent Application Publication JP-A 2003-000543 discloses a configuration of using such an optical image measurement device in the ophthalmic field.
Application of a conventional optical image measurement device in the ophthalmic field may cause problems as described below. First, in a conventional optical image measurement device, in a case where an eye has a site reducing the intensity of a signal light such as a nuclear cataract and a subcapsular cataract in the eye, the signal light is projected to a fundus oculi through this site. Therefore, the intensity of a fundus oculi reflection light of the signal light is decreased, and an interference light with sufficient intensity cannot be detected, with the result that a clear OCT image cannot be acquired. Moreover, the accuracy of an OCT image may decrease resulting from scatter of the signal light at this site.
It may be considered to previously specify such a site and perform position matching (alignment) of the eye with the device so that the signal light is projected avoiding this site. However, since such a preparation work requires a lot of effort, a load on the examiner increases. Moreover, since the examination takes more time, a load on the patient also increases. Especially in the case of performing plural times of measurement at a single site as in an observation of clinical course, it is necessary to perform alignment for every measurement, which is troublesome.
Further, in a conventional optical image measurement device, it is impossible to previously grasp what image will be acquired actually. Therefore, there is a case where measurement is performed in the insufficiently aligned condition and an image is acquired at a site displaced from an observation target such as an optic disk, a macula and a lesion. Consequently, it takes meaningless time and effort for measurement once more.